1. Field of the Application
The present application relates to a method and apparatus for image developing, and more particularly to a method and apparatus for image developing which is capable of effectively forming an even development agent layer on a development agent carrying member.
2. Description of the Background
Generally, development apparatuses that develop an electrostatic latent image formed on an image carrying member can be classified into two types. One type develops an electrostatic latent image formed on an image carrying member with a development roller which is brought into contact with the image carrying member. This type is called a contact development apparatus and its development method is referred to as a contact development method. The other type develops an electrostatic latent image formed on an image carrying member with a development roller brought into proximity to the image carrying member. This type is called a non-contact development apparatus and its development method is referred to as a non-contact development method. It is extremely important for both types of the development apparatuses to stably maintain the relative conditions of the development roller and the image carrying member so as to reproduce a superior quality image.
The contact development apparatus, for example, includes a development roller, a toner supplying roller, and a development blade, as important elements. The development roller develops an electrostatic latent image formed on the image carrying member. The toner supplying roller supplies toner to the development roller. The development blade regulates the toner carrier on the development roller into a thin layer having a predetermined thickness. The development roller is held in contact with the image carrying member under a predetermined pressure applied by an elastic member such as a coil spring.
The development agent used for the development of an electrostatic latent image on the image carrying member can also be classified into two types. One type is referred to as a two component development agent that includes toner and carriers. The other type is referred to as a single component development agent that includes toner. The development method using the two component development agent can reproduce a superior quality image in a relatively stable manner but has disadvantages relating to the carriers. For example, the carriers are prone to be degraded over time and a mixture ratio of the toner and the carriers is varied. In addition, the development apparatus using the two component development agent tends to be a relatively large-sized machine. In order to avoid these disadvantages of the two component development agent, it is more convenient to employ the development method that uses the single component development agent.
In the development method using the single component development agent, however, the development roller needs to be held in contact evenly with the image carrying member in a stable manner. Otherwise, the amount of toner supplied to the image carrying member is unstable, which may cause problematic phenomena such as an uneven density on a formed image or a dirty background.
To reproduce a superior quality image, it is required that the development agent carried on the development roller is made into a thin layer by regulating the contact of the image carrying member and the development roller in an area where the development process is conducted.
A Published Japanese Unexamined Patent Application, No. 60-103372 (1985), attempts to regulate the toner into a thin layer in an even manner with a development apparatus using a roll-shaped toner layer regulating member that includes a roll-shaped rubber surface having hardness in a range of 10 degrees to 40 degrees according to the JIS-A (Japanese Industrial Standard-A). However, it is apparent that this structure is not sufficient to succeed in the attempt. In fact, when a polyurethane rubber of hardness in the range of 10 degrees to 40 degrees JIS-A is used for the toner layer regulating member, it is not possible to form an even and thin toner layer because a friction coefficient of such toner layer regulating member is relatively high.
A Published Japanese Unexamined Patent Application, No. 10-104945 (1998), attempts to form an even toner layer and to accelerate toner charging. This attempt uses a roll-shaped toner layer regulating member having a surface roughness Rz in a range of from 2 xcexcm to 100 xcexcm, and produces an effect of a vibrating electric field by applying a voltage overlaid with an AC (alternating current) bias to the development roller. This attempt, however, is not practical since it has problematic disadvantages. For example, it requires a coating on the surface of the toner layer regulating member with uniform toner particles and a matrix resin because of the surface roughness Rz. Also, this attempt requires a complex configuration which leads to a relatively high manufacturing cost since it uses an AC power source.
FIG. 26 shows a prior art development apparatus that uses a single component development agent. In this prior art development apparatus, a roller-like-shaped development agent carrying member 301 and a roller-like-shaped development agent supplying member 302 are rotated so that development agent contained in a hopper 304 built in a development case 303 is supplied and the development agent is carried on the circumferential surface of the development agent carrying member 301. The development agent carried is formed into a thin layer by a development agent regulating member 305 and is then attracted to an image carrying member (not shown) so that a latent image formed on the image carrying member is developed into a visual image.
The development agent regulating member 305 has, in many cases, a blade-like shape, as shown in FIG. 26, and brings its edge into contact with the development agent carrying member 301 so as to regulate a thickness of the development agent carried. A development agent regulating member including a layer of an elastic substance such as a urethane rubber is applied to a case in which the development agent carrying member includes a hard roller made of a metal or plastic. A metallic development agent regulating member is applied to a case in which the development agent carrying member includes an elastic roller made of rubber.
In a development apparatus using the above blade-shaped development agent regulating member 305, the development agent is subjected to a friction charging process in a nip band region formed between the development agent carrying member and the development agent regulating member. However, the surface of the development agent is prone to be worn over time because of the friction charging process and therefore the charge capacity of the development agent is reduced. As a result, the charge amount on the development agent is reduced which causes problematic phenomena such as a dirty background, failed development of fine dots, etc.
Also, the development agent is prone to melt in the nip band region due to heating caused through the friction charging process. When the melted development agent fixes on the development agent regulating member, it causes a line mark on the development agent carrying member. This causes a problematic white line mark on a recording sheet, as a result.
In addition, foreign substances such as dust particles are prone to be lodged between the development agent carrying member and the development agent regulating member and such lodged foreign substances may cause the above-described white line marks on a recording sheet. A cause of this is in a structure in which the blade-shaped development agent regulating member 305 is fixed with its base edge to the development case 303 such that the top edge thereof contacts the circumferential surface of the development agent carrying member 301 under pressure.
The above-described problems, in many cases, occur in a relatively short time period and they are not easily recovered from when they occur. Accordingly, the life time of the development apparatus is shortened and the development apparatus needs to be frequently exchanged, which increases a user""s burden with respect to time and cost. In particular, the blade-shaped development agent regulating member is not a realistic solution for a high speed printing apparatus.
Published Japanese Unexamined Patent Applications, No. JP09-80905 (1997) and No. JP11-84867 (1999), provide exemplary descriptions of prior art development apparatus using roller-shaped development agent regulating members. As shown in FIG. 27, a development agent regulating member 406 includes a shaft 407 supported by supporters 408. The supporters 408 are pressed by pressing members 409 so that the development agent regulating member 406 contacts a development agent carrying member 401 under pressure while rotating in the direction opposite to the rotation direction of the development agent carrying member 401.
In these development apparatus, the roller-like-shaped development agent regulating member 406 is rotated, and it is therefore possible to reduce the occurrence of an event where a foreign particle such as dust is lodged between the development agent carrying member 401 and the development agent regulating member 406.
However, in an image forming apparatus capable of using a large-sized recording sheet (i.e., an A3 size sheet), the development agent regulating member 406 as well as the development agent carrying member 401 necessarily have sufficiently long lengths. Accordingly, the development agent regulating member 406 is prone to be bent when the shaft 407 is pressed by the pressing members 409. When the development agent carrying member 401 is rotated, it pulls the development agent regulating member 406 which is therefore further bent. As a result, the development agent regulating member 406 generates a gap d at the center in the axial direction relative to the development agent carrying member 401, as shown in FIG. 28.
In this case, the pressure of the development agent regulating member 406 relative to the development agent carrying member 401 becomes uneven and, as a result, the layer of the development agent on the development agent carrying member 401 becomes uneven and thick around the center, as shown in FIG. 29. In addition, the charge amount of the development agent becomes extremely low around the center in the axial direction, as shown in FIG. 30. These abnormal conditions lead problematic phenomenon such as a toner dispersion inside the apparatus, etc.
In order to reduce the gap d shown in FIG. 28, the axial diameter of the shaft 407 may be made thicker. However, the shaft 407, even if it is made of steel, is needed to have a diameter of 15 mm or thicker and becomes extremely heavy. This leads to an inevitable necessity of making the whole apparatus.
The present application describes a novel development apparatus. In one example, a novel development apparatus includes a development roller, a supplying roller, and a toner layer regulating member. The development roller is configured to contact an image carrying member and to develop an electrostatic latent image into a toner image on the image carrying member. In this case, the development roller is made of aluminum and is rotatably mounted in the apparatus. The supplying roller configured to supply toner to the development roller. The toner layer regulating member is configured to regulate the toner to form a thin film on the development roller. In this example, the toner layer regulating member has a roller shape, a surface roughness Rz in a range of from 0.5 xcexcm to 2 xcexcm, and a dynamic friction coefficient in a range of from 0.1 to 0.8.
The toner may have a volume average particle diameter in a range of from 6 xcexcm to 9 xcexcm.
The development roller may have a surface coated with an anodized aluminum film, a surface subjected to an electroless nickel plating, a surface subjected to a nitriding processing, or a surface coated with a melamine resin.
Further, the present application describes a novel development agent layer regulator. In one example, a novel development agent layer regulator includes a roller which is configured to contact a member for carrying a development agent and to form a thin film of the development agent on the member. This roller has a diameter around a center portion thereof greater than a diameter around end portions thereof and a symmetrical shape about a center line perpendicular to an axis thereof.
Further, the present application describes a novel development apparatus. In one example, a novel development apparatus includes a roller which is configured to contact a member for carrying a development agent and to form a thin film of the development agent on the member. This roller has a diameter around a center portion thereof greater than a diameter around end portions thereof and a symmetrical shape about a center line perpendicular to an axis thereof.
In the above-described development apparatus, a diameter of the roller may be linearly reduced from the center line towards the both end portions, or the diameter of the roller may be of constant within a predetermined width in the center portion and is linearly reduced from edges of the center portion towards both end portions.
In the above-described development apparatus, a length of the roller in an axial direction may be divided into a plurality of sections, a diameter of the roller in each section may be linearly reduced towards the end portion, and angles of slanting line segments formed by the diameters in the plurality of sections relative to the axis of the roller may be stepwise reduced towards the end portions.
The diameters on division lines at which the length of the roller is divided may be set on a single quadric curve or on a single circular arc.
In the above-described development apparatus, an intersection point of adjacent two slanting line segments among the slanting line segments formed by the diameters in the plurality of sections may meet a single circular arc of a predetermined radius.
The slanting line segments formed by the diameters in the plurality of sections may be tangential to a single quadric curve or to a single circular arc.
In the above-described development apparatus, more than one of the diameters on division lines at which the length of the roller is divided may be set on a single quadric curve and more than one of the slanting line segments formed by the diameters in the plurality of sections may be tangential to the same single quadric curve.
In the above-described development apparatus, more than one of the diameters on division lines at which the length of the roller is divided may be set on a single circular arc and more than one of the slanting line segments formed by the diameters in the plurality of sections may be tangent to the same single circular arc.
The diameter of the roller may be varied in the axial direction in accordance with a specific curve of a variant to a fourth power, in accordance with a quadric curve, or in accordance with a circular arc.
In the above-described development apparatus, tangential lines of the specific curve may be used as line segments for both sides of the specific curve so that the diameter of the roller is made relatively greater in both end portions.
In the above-described development apparatus, both end portions of a different curve that touches the specific curve may be used as line segments for both sides of the specific curve so that the diameter of the roller is made relatively greater in both end portions.
The roller may include an elastic layer.
The development agent may include a single component.
Further, the present application describes a novel process cartridge. In one example, a novel process cartridge include a development apparatus which includes a roller. The roller is configured to have a diameter around a center portion thereof greater than a diameter around end portions thereof and to have a symmetrical shape about a center line perpendicular to an axis thereof. The roller contacts a member for carrying a development agent and forms a thin film of the development agent on the member. The process cartridge is detachably installable into an image forming apparatus.
Further, the present application describes a novel image forming apparatus. In one example, a novel image forming apparatus a development apparatus which includes a roller. The roller is configured to have a diameter around a center portion thereof greater than a diameter around end portions thereof and to have a symmetrical shape about a center line perpendicular to an axis thereof. The roller contacts a member for carrying a development agent and forms a thin film of the development agent on the member.